Emissions control system

ABSTRACT

A method, system and apparatus for minimizing the amounts of undesirable pollutants emitted from an internal combustion engine after combustion of a fuel-air mixture within a cylinder of said engine in which a portion of the products of combustion of a given operating cycle, which portion contains a higher proportion of noxious constituents than does the expelled portion of such products, is retained in the cylinder and is mixed with the incoming charge for the next operating cycle. One particular form of the invention comprises varying the proportion of such retained products according to engine operating conditions in order to maintain the dilution of such incoming charge at the maximum level consistent with good engine performance. The retained products are in an amount in excess of that normally retained in the cylinder clearance volume at the exhaust manifold pressure.

United States Patent Meacham et al. 1 1 Feb. 6, 1973 [5 1 EMISSIONS CONTROL SYSTEM 3,441,009 4 1969 Rafanelli ..123/90.15 [75] Inventors: George B K. Meacham, l 3,494,336 2/1970 Meyers et al. ..l23/90.l5 X

N 1 gi x f g S age Primary Examiner-Al Lawrence Smith Attorney-Donald L. Wood [73] Assignee: Eaton Yale & Towne Inc., Cleveg1 d ,9l 19 j 57 ABSTRACT [22] Filed: 1971 A method, system and apparatus for minimizing the [21] Appl. No.: 173,068 amounts of undesirable pollutants emitted from an internal combustion engine after combustion of a fuel- Related Apphcguon Data air mixture within a cylinder of said engine in which a [63] Continuation of Ser. No. 746,644, July 22, 1968, Portion of the Products of combustion a given abandoned. operating cycle, which portion contains a higher proportion of noxious constituents than does the expelled [52] US. Cl v.123/75 E, 64/25, l23/90.l5 portion of such products, is retained in the cylinder [51] Int. Cl. ..F01ll/34, F02d 39/02 and is mixed with the incoming charge for the next [58] Field of Search ..l23/90.l5-90.l8, operating cycle. One particular form of the invention 123/75 R, 75 E, 97 R, 97 B, 107, 119 A; comprises varying the proportion of such retained 64/25 products according to engine operating conditions in order to maintain the dilution of such incoming charge [56] References Cited at the maximum level consistent with good engine performance. The retained products are in an amount in UNITED STATES PATENTS excess of that normally retained in the cylinder 2,191,459 2/1940 Duncan ..123 90.17 defiance volume at the exhaust manifold Pressure- 3,l44,009 8/1964 Goodfellow et al. ......l23/9O.l7 3,166,057 1/1965 Konrad et al... ..123 90..15 14 Claims, 9 D'awlng Flgures 3,262,435 7/1966 Cribbs ..l23/90.l5

INCOMPLETELY BURN ED HYDPOCAPBON CONCENTPATION EXHAUST AND gCLOSES (s10) VOLUMUEK; VOLUMETQlC DATE OF RATE OF DISCHAPGEOF DISCHAPGE EXHAUST GASES EXHAUST 'CLOSES (ADV) INCOMPLEYELY 4 "TPAPDED 15111211129 APEA nvoeocmesm QONCENTEATWN F CRANK sum EXHAUST Berton, DEGPEES OF 190mm op VALVE DEAD DEAD OPENS CENTER CENTEQ PATENTEDFEB s I SHEET 10F 4 INCOMPLETELV sweuw HYDDOCAPBON CONCENTPATION EXHAUST AND 50mm (STD) VOLUMETEIC VOLUMETQIC PATE OF RATE OF DISCHAPGEOF DISCHAPGE EXHAUST GASES EXHAUST CLOSES (ADV) mcowmaw TPAPPED BU PNED APEA HYDEOCAPBON \coucmwmou UBANK SHAFT EXHAUST BOTTOM DEGREES OF POTAUON op W D DEAD QPENS CENTER CENTEQ PRIOR ART I A I l H- l5 INVENTORS 4 wow! ,5? A. Mum/4 07" BY M10444 5. fl/lfl PATENTEDFEB elm 3,714,932

SHEET 2 OF 4 CONVENTIONAL VALVE TIMING mc FULLY OPEN EXHAUST UNTAKE VALVE I VALVE PRIOR/212T -|5| I+L5 CEANKSHAFT W DEGREES OF POTATION OVEPLAP- ADVANCED VALVE TIMING- SAME OVEPLAP TDC I FULLY OPEN INTAKE VALVE 4 w- ON OVER-LAP D 0 A FuLLV TDC [Cliff OPEN l I EEANKSHAFT' DEGQEES 0F POTATION ADVANCED ExHAusT VALVE CLOSING N0 VALVE OVEELAP- E TENED VALVE OVEELAP INVENTORS I azowz 5/( 416407441 Y W/LU/IM 6 A/AOZL EMISSIONS CONTROL SYSTEM CROSS REFERENCE TO RELATED APPLICATION This application is a continuation of our application Ser. No. 746 644, filed July 22, 1968, now abandoned, and entitled Method and Apparatus For Controlling Emissions From An Internal Combustion Engine.

FIELD OF THE INVENTION This invention relates to a method, system and apparatus for controlling the exhaust gas emissions of internal combustion engines and, more particularly, re-

BACKGROUND OF THE INVENTION Noxious exhaust gas emissions of internal combustion engines, particularly engines in motor vehicles, are an important cause of air pollution. It is desired, therefore, to minimize such noxious exhaust gas emissions and great amounts of effort have been and are being expended in attempts to do so.

Noxious exhaust gas emissions from internal combustion engines fall into two general classes, namely, (1) those which are the result of incomplete combustion of the hydrocarbon fuel and (2) those which are formed by the reaction between nonfuel components present in the combustion chamber. The latter class of noxious exhaust gas emissions are generally various compounds of nitrogen and oxygen and these compounds will hereinafter be referred to generally by the designation nitrogen oxides.

With respect to the noxious exhaust gas emissions resulting from incomplete combustion of the hydrocarbon fuel, there are several mechanisms responsible for such incomplete combustion. One such mechanism results from the use of an excessively rich fuel-air mixture which results in a relatively high proportion of unburned hydrocarbons and large amounts of carbon monoxide in the exhaust gas. This can be corrected by careful manifold design, which gives good distribution of the fuel-air mixture and allows leaner carburetor calibration. Further, leaning out the mixture by using a lower ratio of fuel to the combustion air in the fuel-air mixture will improve the completeness of combustion. In particular, leaning out the mixture will reduce the carbon monoxide to a low level. However, both the carbon monoxide and the unburned hydrocarbons in the exhaust gas will be decreased only slightly as the mixture is made leaner than stoichiometric, that is, if an excess of air is supplied over and above that needed for complete combustion of the fuel. Actually, the amounts of carbon monoxide and unburned hydrocarbons in the exhaust gas will start to increase as the fuelair mixture is leaned out toward the point at which the engine will start to misfire.

A second major mechanism contributing to the presence of the unburned hydrocarbons in the exhaust gas is the quenching of the flame front following ignition of the fuel-air mixture as the flame front approaches the relatively cool surfaces of the cylinder and the piston. This quenching causes a boundary layer of unburned and partially burned fuel-air mixture to be left on or adjacent these relatively cool surfaces after the flame front has passed. Much of this layer is subsequently expelled into the exhaust system during the exhaust stroke. The occurrence of the boundary layer of the unburned and partially burned fuel-air mixture can be reduced to some extent by designing a more compact combustion chamber with a smaller surfaceto-volume ratio, which results in less boundary layer area, and/or by causing swirl or turbulence ofthe fuelair mixture to provide better mixing, which results in a thinner boundary layer. However, there are definite practical limits on the effectiveness of these techniques.

The temperature of the exhaust gas as it is expelled through the exhaust port into the exhaust manifold and its residence time at an elevated temperature in the exhaust system can also have an important influence on the composition of the exhaust gas emissions. Much of the carbon monoxide and unburned hydrocarbons in the exhaust gas can be consumed in the exhaust gas system if the temperature is high enough, the retention time of the exhaust gas in the exhaust system is long enough and if there is oxygen present in the exhaust system. Oxygen can be provided in the exhaust gas system either by supplying a leaner than stoichiometric mixture to the cylinder or by forced injection of fresh air into the exhaust system. Higher temperatures in the exhaust system can be maintained for a longer time by insulating the surfaces in the exhaust gas system which are in contact with the exhaust gases. The temperature of the exhaust gas as it exits from the cylinder can also be increased to some extent by retarding the spark or by opening the exhaust valve earlier in the expansion stroke.

exhaust valve during the valve overlap period. As used herein, the term "valve overlap period, or derivatives thereof, refers to the time during which both the intake valve and the exhaust valve for a given cylinder are open at the end of an exhaust stroke, and at the beginning of an intake stroke. At this time, the exhaust manifold is at or near atmospheric pressure and the inlet manifold and the cylinder are substantially below atmospheric pressure. This causes exhaust gas to be drawn back into the cylinder from the exhaust manifold and thereby dilutes the incoming fuel-air mixture. This dilution, in combination with the low flame propagation speed at low temperature, results in poor combustion in the cylinder, thereby causing a high concentration of unburned hydrocarbons and carbon monoxide in the exhaust gas.

An important consequence of the presence of the boundary layer of the incompletely burned fuel-air mixture in the cylinder is that the concentration of the noxious exhaust gas components is not uniform throughout the exhaust stroke. During the early and middle portions of the exhaust stroke, the exhaust gas flowing into the exhaust manifold is primarily from the center of the cylinder volume where no flame front quenching occurs. As a result, the combustion of the fuel-air mixture in the central portion of the cylinder volume is fairly complete and this portion of the exhaust gases is relatively free of hydrocarbon and carbon monoxide exhaust gas components. However, during the latter part of the exhaust stroke, the layer of gas near the cylinder walls is expelled. Since this layer contains a relatively high proportion of unburned hydrocarbons, the concentration of the hydrocarbon and carbon monoxide exhaust gas components in the exhaust gasrises to a very high level during the latter part of the exhaust stroke.

Considering now the nonfuel noxious exhaust gas components, which essentially are formed by the reaction of nitrogen and oxygen at the high temperature of combustion, the main controlling parameters which determine the concentration of the nitrogen oxides in the exhaust gas are the peak cycle temperature in the cylinder and the available oxygen. A substantial excess of nitrogen is always present in the fuel-air mixture so that nitrogen cannot be controlled. The lean mixtures which may be employed in order to reduce carbon monoxide and unburned hydrocarbons in the exhaust gas, as discussed above, provide excess oxygen. The consequence of this is that the use of lean mixtures tends to increase the formation of nitrogen oxides. The high compression ratios in common use in automotive engines result in high combustion temperatures and, therefore, relatively high nitrogen oxide formation. This cannot be reduced without simultaneously reducing power or decreasing efficiency, neither of which is acceptable.

It has been previously suggested to control the amount of nitrogen oxides in the exhaust gas by recirculating a portion of the exhaust gas back to the inlet system in order to dilute the fresh fuel-air charge. Since the exhaust gas is relatively inert, this dilution reduces the peak flame temperature in the cylinder and, consequently, the rate of forming nitrogen oxides is diminished.

The systems suggested in the prior art for recirculating exhaust gas to the incoming fuel-air charge commonly employ cooling means, fresh air mixing means and metering means. Although systems of this type can result in some improvement in the quality of the exhaust gases, the necessary conduits, valves, etc. can be quite complex and such equipment is subject to condensation, fouling and corrosion, which make the use of such systems less than completely satisfactory.

Accordingly, a need exists for a procedure for reducing noxious exhaust gas emissions from internal combustion engines, which procedure will minimize the amounts of carbon monoxide, unburned hydrocarbons and nitrogen oxides in the exhaust gases and which will Accordingly, it is an object of this invention to pro vide a method, system and apparatus of reducing noxious exhaust gas emissions from internal combustion engines which, in general, involves varying the normal exhaust and intake timing events in the internal combustion engine, such as by varying the times of opening I and closing the intake and exhaust valves in a fourcycle internal combustion engine, so that a selectable amount of exhaust gas is retained in the cylinder and is mixed with the incoming fresh fuel-air charge to provide a combustible mixture of improved characteristics and thereby simultaneously minimizing the expulsion from the cylinder of noxious exhaust gas components by retaining that portion of the exhaust gas which contains a relatively high amount of noxious components for further combustion in the cylinder It is a further object of this invention to provide a method, system and apparatus as aforesaid, in which the exhaust and intake timing events are varied by closing the exhaust means at different selected times before the end of the exhaust stroke in order to retain a final portion of the exhaust gas in the cylinder, said final portion containing a relatively high proportion of noxious components.

' It is a further object of the invention to provide a method, system and apparatus as aforesaid, in which the variation of the exhaust and intake timing events may include changing the duration of the overlap period for the intake and exhaust means.

It is a further object of the invention to provide a method, system and apparatus as aforesaid, in which the variation of the exhaust and intake timing events can be effected by changing the phase angle between the crankshaft and the exhaust actuating or control means of the engine.

It is a further object of the invention to provide a method, system and apparatus as aforesaid, in which the exhaust and intake timing events can be varied in response to engine operating conditions.

It is a further object of the invention to provide a method, system and apparatus as aforesaid, in which a control system can be provided to vary the exhaust and intake timing events in response to engine operating conditions to provide (1) low dilution of the incoming fuel-air charge at low engine loads, (2) a higher dilution of the incoming fuel-air charge at higher engine loads and, if desired, (3) a low dilution of the incoming do so without appreciably increasing the manufacturfuel-air charge at maximum engine loads.

A further object of the invention is to provide a method, system and apparatus as aforesaid, which does not require the use of additional conduits, valves and the like in the exhaust gas system of the engine and wherein the variation of the exhaust and intake timing events can be effected by known procedures without major alterations of the engine structure whereby the cost of providing the improved timing method of the invention is minimized and also engine maintenance is minimized.

Additional objects and advantages of the invention will become apparent to persons acquainted with equipment of this typeupon reading the following disclosure and inspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph illustrating (1) the concentration of the incompletely burned hydrocarbons in the exhaust gas and (2) the volumetric rate of discharge of the exhaust gas vs. the position of the piston in the cylinder in a typical internal combustion engine. I

FIG. 2 is a schematic view of a cylinder of a fourcycle internal combustion engine and indicating by broken lines the portion of the combustion gas that tends to escape first through the exhaust port.

FIG. 3 is a graph illustrating the opening time of the engine intake valve and the closing time of the engine exhaust valve at the end of the exhaust stroke during conventional four-cycle internal combustion engine operation using a 30 valve overlap period.

FIG. 4 is a graph similar to FIG. 3 and illustratingthe opening and closing times of the engine intake and exhaust valves as they occur under advanced valve closing conditions according to the present invention, while maintaining a 30 overlap period.

FIG. 5 is a graph similar to FIG. 3 and illustrating the opening and closing times of the engine intake and exhaust valves in accordance with modified advanced valve closing conditions according to the present invention.

FIG. 6 is a schematic central sectional view of an apparatus for adjusting the phase relationship of the intake and exhaust valve camshafts with respectto the crankshaft of a four-cycle internal combustion engine.

FIG. 7 is a view similar to FIG. 6 and showing a modified structure in which the phase relationship between the exhaust valve camshaft is adjusted with respect to the engine crankshaft and the intake valve camshaft.

FIG. 8 is a schematic view of one form of control mechanism for controlling the phase relation of a camshaft with respect to the crankshaft of a four-cycle internal combustion engine.

FIG. 9 is a schematic view of another control system for adjusting the phase relation between the camshaft and the engine crankshaft of a four-cycle internal combustion engine.

SUMMARY OF THE INVENTION According to the present invention, there is provided a method, system and apparatus for minimizing the concentrations of both the incompletely burned hydrocarbons and the nitrogen oxides in the exhaust gas of an internal combustion engine. The method, system and apparatus involves closing the exhaust means of each cylinder of the engine a selectable period of time before the piston in that cylinder moves from its top dead center position on its fuel intake stroke sufficiently that the gas pressure at the piston head equals (more precisely begins to be less than) the pressure in the exhaust manifold in order to trap within the cylinder a selected volume of the exhaust gas, which volume contains a relatively high concentration of the incompletely burned fuel from the previous ignition step. The intake means for the cylinder is opened at, or a selectable period of time before, the time the exhaust means is closed in order to supply a fresh I charge of unburned fuel and air into the cylinder. The retained exhaust gas and the fresh charge are'mixed with each other in the cylinder and the mixture is subsequently ignited in the following cycle of operation of the engine. The incompletely burned fuel in the exhaust gas retained in the cylinder is therefore subject to recombustion. Moreover, the retained exhaust gas dilutes the incoming fresh charge of unburned fuel and air entering the cylinder and this has the effect of reducing the peak cycle temperature during the next cycle of operation of the engine. This in turn minimizes the formation of nitrogen oxides. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description will refer to the application of the invention to a four-stroke cycle, spark-ignited reciprocating internal combustion engine, for purposes of describing preferred embodiments of the invention, and therefore the description will refer to the intake valve and the exhaust valve which are used to control the intake and exhaust functions. It will be understood, however, that the invention is also applicable to two-cycle and other ported engines, diesel engines, and other engines which involve the intermittent timed intake of fuel and air into a combustion chamber and the intermittent timed, exhausting of the products of combustion from the combustion chamber. Intake and exhaust valves may or may not be used therein. The terms exhaust means and timing means used in the claims shall refer to the means, such as the valves in the disclosed embodiments, which effect the exhausting of the products of combustion and the supplying of the fuel and air to the combustion chamber, respectively. Similarly, for convenience in description, the following description will also refer to the top dead center position of the piston in the cylinder in order to identify a convenient and precise reference point with respect to which the exhaust and intake timing events are adjusted. When the piston is at the top dead center position at the end of its exhaust stroke, the gases in the clearance volume between the head of the piston and the top wall of the cylinder are at a higher pressure than the pressure in the exhaust manifold. This condition continues to exist for a minute period of time after the piston begins to move away from the top dead center position on its fuel intake stroke (whether the fuel intake is by suction or by injection). The time at which there is a reversal of the pressure levels within the cylinder and exhaust manifold, such that the gas pressure at the piston head equals (begins to be less than) the pressure in the exhaust manifold, determines the exact reference point with respect to which the exhaust and intake timing events are adjusted and the following description will be understood accordingly.

Referring to FIG. 1, there is illustrated a graph of l) the concentration of the incompletely burned hydrocarbons in the exhaust gas of a typical internal combustion engine and (2) the volumetric rate of flow of the exhaust gas with respect to the position of the piston within the cylinder. It has been observed that, in the normal operation of internal combustion engines, the concentration of the incompletely burned hydrocarbons in the exhaust gas exiting from the cylinder remains at a relatively low level until the piston approaches its top dead center (TDC) position within the cylinder bore. As the piston approaches its top dead center position, the concentration of the incompletely burned hydrocarbons in the exhaust gas rises sharply. An explanation for this phenomenon will be given below. It will also be noted that the volumetric opened due to the relatively high pressurev in the cylinder. After the volumetric rate of discharge reaches a peak, it gradually diminishes as the pressure within the cylinder becomes reduced so that toward the end of the discharge stroke the discharge of the exhaust gas is effected essentially by displacement thereof by the piston. The hatched area of FIG. 1 indicates the amount of exhaust gas that is retained in the cylinder when the exhaust valve is closed before the end of the exhaust stroke according to this invention.

FIG. 2 illustrates a conventional piston and cylinder assembly of an internal combustion engine comprising a reciprocating piston 11 which is slideable within a cylinder bore 12. Intake and exhaust valves 13 and 14 are provided at the upper end of the bore. A crankshaft 15 is coupled to the piston 11 by the rod 16in the usual fashion.

The following is offered as an explanation of the fact that the final portion of the exhaust gas discharged from the cylinder contains a relatively high concentration of incompletely burned hydrocarbons. It is to be understood, however, that the improved results achieved by this invention have been actually observed and measured and hence the invention itself is not dependent on the correctness of this explanation.

The zone A (FIG. 2) located in the central portion of the cylinder contains gas which is in a relatively more completely burned state and which is at a relatively higher temperature. The gas outside the zone A is at a lower temperature because it is close to the relatively cool walls of the cylinder and piston. The latter gas is also less completely burned because the flame front of the fuel-air mixture, when same is ignited, is quenched as it approaches, these walls so that the combustion of the fuel adjacent the walls of the cylinder and piston is less complete. The gas outside zone A tends to remain in the cylinder until it is forced therefrom by displacement by the piston as the piston approaches the top dead center position thereof. For this reason the gas initially discharged during an exhaust stroke is primarily from zone A whereas the final quantity of exhaust gas discharged from the cylinder contains a relatively high proportion of gas from outside the zone A, which gas contains a relatively larger concentration of incompletely burned hydrocarbons.

Although the zone A has been illustrated as being sharply defined, this has been done for the purposes of ease of illustration and explanation. It will be apparent that in reality there will be a gradual increase in the concentration of the incompletely burned hydrocarbons and also a gradual decrease in the temperature of the gas, as the walls of the cylinder and piston are approached. Moreover, the zone A has been shown as being of relatively small volume again for ease of illustration and explanation. Actually, Zone A will extend quite close to the walls of the cylinder and piston.

In FIG. 3, there is illustrated a graph of a portion of a conventional valve timing procedure for a four-cycle internal combustion. As illustrated in this FIGURE, the exhaust valve starts to move toward its closed position shortly before the top dead center (TDC) position of the piston within the cylinder and said exhaust valve reaches its fully closed position at about 15 degrees of crankshaft rotation following the top dead center position of the piston. The intake valve starts to open approximately 15 before the top dead center position and reaches a fully opened position after the top dead center position of the piston has been passed. The period between the start of the intake valve opening and the finish of the exhaust valve closing is the valve overlap period. Such a valve overlap period is required for well-understood reasons in order to provide, the

desired operating characteristics of the engine. The

' length of the valve overlap period can be varied from one engine design to another for various purposes, such as to achieve a high performance operation or relatively great fuel economy. It is known to provide valve overlap periods ranging from about 14 to about of engine crankshaft rotation for various automotive engine designs.

According to one embodiment of the invention, all of the valve timing events of the internal combustion engine can be advanced by equal amounts, without changing the valve overlap period, so that the exhaust valve closes at or before the piston reaches its top dead center position. This is illustrated in FIG. 4, in which the exhaust valve closing time has been advanced so that the exhaust valve closes at 5 before the top dead center position. The inlet valve, therefore, begins to open at about 35 before the top dead-center position. The valve overlap period therefore remains constant at 30 of engine crankshaft rotation. This advancement of the valve timing events has the effect of trapping an increased volume of the exhaust gas of a given cycle of operation of the engine within the cylinder.

Even without advancing the valve timing events, some of the exhaust gas is usually retained within the cylinder because of the clearance volume between the top dead center position of the piston and the cylinder head. However, the advancement of the exhaust valve closing time causes an even greater volume of exhaust gas to be retained within the cylinder. This extra volume of trapped exhaust gas contains a relatively high concentration of the incompletely burned hydrocarbons. This trapped exhaust gas is subject to recombustion in the following cycle of operation of the engine to thereby reduce the incompletely burned hydrocarbons that enter the exhaust manifold.- Also, the retained exhaust gas is mixed with and dilutes the incoming fuel-air charge from the intake manifold. Since the trapped exhaust gas contains a substantial concentration of noncombustible gases, this reduces the peak cycle temperature in the following cycle of operation of the engine. This in turn has the effect of minimizing the formation of nitrogen oxides because, as pointed out previously, lower peak cycle temperatures reduce the formation of such products. Thus, the advancement of the exhaust valve closing time has the effect of reducing the pollutants in the exhaust gas entering the exhaust gas manifold.

The effect of the present invention is'to trap in the cylinder a relatively small volume of exhaust gas, but this volume of exhaust gas is selected to contain a relatively high proportion of unburned hydrocarbons so that the amount of unburned hydrocarbons reaching the exhaust manifold is substantially reduced. The

amount of the trapped exhaust gas retained in the cylinder is represented by the hatched area in FIG. 1

and from this it will be seen that the effect of the invention is to prevent a very substantial amount of the total incompletely burned hydrocarbons in the exhaust gas from entering the exhaust gas manifold.

The advancement of all of the valve timing events of the engine also advances the exhaust valve opening time, the intake valve opening time and the intake valve closing time. The earlier opening of the intake valve as illustrated in FIG. 4, has been found not to significantly affect the operation of the engine. However, as will be pointed out below, it may be desirable not to advance the intake valve opening time when the exhaust valve closing time is advanced during certain conditions of operation of the engine in order to effect a further minimizing of the pollutants entering the exhaust gas manifold. The earlier closing of the intake valve and the earlier opening of the exhaust valve, when all of the valve timing events are advanced as described above, has been found to have little or no measurableeffect on the operation of the engine.

The advancement of all of the valve timing events in the internal combustion engine can be effected by changing the phase relationship between the engine crankshaft, on the one hand, and the intake valve camshaft and the exhaust valve camshaft, on the other hand. This can be done by hand when the engine is stopped or it can be done while the engine is in operation in any suitable way, such as by the mechanisms to be described below.

Referring to FIG. 5, there are illustrated two additional ways by which the invention can be carried out in practice. As is the case with FIG. 4, the exhaust valve closing time is shown as being advanced to five degrees ,before the top dead center position of the piston. As indicated by the short dashed lines, the intake valve closing time can be maintained unchanged, in which case the valve overlap period is shortened to 10 of crankshaft rotation. Further, as illustrated by the longshort dashed line in FIG. 5, the valve timing events can be adjusted so that exhaust valve closes at the same time that the intake valve opens so that there is no overlap period.

It may be desired to shift the valve timing events during operation of the engine between the timing condition illustrated in FIG. 4 and one of the timing conditions illustrated in FIG. 5 as the operating conditions of the engine change. In particular, it may be desired to operate the engine under the timing conditions illustrated in FIG. 4 during constant speed or moderate acceleration engine operating conditions and it may be desired to operate the engine under one or the other of the timing conditions illustrated in FIG. 5 during idling, deceleration, maximum load'or maximum acceleration conditions ofthe engine.

During idling, deceleration or low load operation of the engine, the engine operates under relatively low pressures and temperatures so that the likelihood of nitrogen oxide formation is relatively low.

Further, if the amount of trapped gases is too large at light engine loadings, misfiring of the engine can occur. Therefore, it is both feasible and desirable under conditions of light engine loading to trap onlya relatively small amount of exhaust gas in a cylinder at the end of an exhaust stroke. This can be done by shortening the valve overlap period or by closing the exhaust valve at or very near the top dead-center position of the piston.

It is similarly desirable to effect relatively low dilution ofthe incoming fuel-air charge for maximum load or acceleration conditions. In this instance, however, the low dilution is required in order to obtain the necessary power output from the engine or, otherwise stated, because an excessive dilution of the incoming fuel-air mixture under conditions of heavy engine loads will result in impaired power output and engine knock. Again, the appropriate exhaust gas retention can be selected by appropriate adjustment of valve timing means, namely, by reducing the valve overlap period or by closing the exhaust valve at or near the top deadcenterposition of the piston at the end of its exhaust stroke or at the beginning of its fuel intake stroke. The amount of exhaust gases retained as the engine loading approaches maximum load will therefore be less than the amount of exhaust gas retained at intermediate engine loads and may often be of a magnitude generally similar to that retained for light loadings or idling conditions. Specifically, however, the amount of exhaust gas retained at heavy engine loadings may be less than, equal to or slightly greater than the amount of exhaust gas retained at light engine loadings.

Thus, the volume of exhaust gas retention will be relatively small at light engine loadings, substantially larger at intermediate engine loadings and again small at heavy engine loadings or under conditions of substantial acceleration. Thus, the valve timing events should be appropriately modified to carry out such variations in the exhaust gas retention and for obvious reasons, it is possible that such variations in the exhaust valve timing should be effected automatically. Thus, the maximum advance of exhaust valve closing time must be selected so that the volume of exhaust gas trapped in the cylinder at any one time is as much as possible under the particular engine operating conditions at such time but must be less than that which under such engine operating conditions would cause an excessive dilution of the incoming fuel-air charge. In a given case, of course, the maximum advance that is permissible will depend upon the design of the engine, including the clearance volume and the shape of the piston and cylinder. In general, the maximum advance of the exhaust valve closing time should not exceed 25 of engine crankshaft rotation before the top dead center position of the piston within the cylinder.

In all cases, the exhaust valve should be closed at a limit point before there occurs a reversal of the pressure levels between the gases within the cylinder and above the piston, elsewhere herein referred to as the gases at the piston head and the gases within the exhaust manifold. This limit point is preferable in order to avoid drawback of gases from the exhaust manifold into the cylinder. Such limit point is for all practical purposes the point at which the pressures within the cylinder and within the exhaust manifold are equal but may be more precisely defined as the point before the pressure above the piston head begins to be less than the pressure in the exhaust manifold.

As indicated above, it will be desirable to adjust the valve timing events while the engine is in operation, particularly automatically in response to engine operating conditions. A variety of mechanisms can be provided for this purpose. FIG. 6 schematically illustrates a mechanism by which both the intake valve camshaft and the exhaust valve camshaft can be simultaneously adjusted in equal amounts in order to adjust all of the valve timing events with respect to the top dead center position of the piston in the cylinder.

The intake valve camshaft 21 is coupled for synchronous rotation with the exhaust valve camshaft 22 by means of gears 23 and 24. The exhaust valve camshaft 22 has a slot 26 which is inclined with respect to the axis of rotation of said camshaft. A drive shaft 27 has a radial pin 28 which extends into the slot whereby axial movement of the shaft 27 will effect angular movement of the camshaft 22 about its axis of rotation. Because of the driving interconnection provided by the gears 23 and 24, a corresponding angular movement of the intake valve camshaft 21 will take place. A gear 30 is mounted on the drive shaft 27 and said gear has a splined connection with a further gear 29. The further gear 29 is driven from the crankshaft of the engine in a conventional fashion. Ordinarily, the shaft 27 and thereby the shafts 21 and 22 will be rotated at one-half the crankshaft speed.

A control input of any suitable type, such as those to be described below, can be applied to move the shaft 27 axially and thereby adjust phase relation between the camshafts 21 and 22, on the one hand, and the engine crankshaft, on the other hand. However, the camshafts 21 and 22 at all times remain drivingly connected to the crankshaft for simultaneous rotation therewith.

FIG. 7 illustrates a modified structure by which the phase relation of only the exhaust valve camshaft can be adjusted with respect to the engine crankshaft. The

phase relation between the intake valve camshaft and the engine crankshaft will not be changed. The mechanism illustrated in FIG. 7 is generally similar to the mechanism illustrated in FIG. 6 and corresponding parts are indicated by the same reference numerals with the suffix A applied thereto. The foregoing description of FIG. 6 also applies in substance to the embodiment illustrated in FIG. 7. It will be noted, however, that gear 24A is mounted on shaft 27A, instead of shaft 22A, so that axial movement of the shaft 27A will effect angular movement of only the shaft 22A. Thus, only the exhaust valve camshaft 22A will be rotated with respect to the engine crankshaft in response to the control input applied to shaft 27A. It will also be noted that gear 23A has a spline connection with gear 24A so as to maintain a continuous driving connection therebetween while permitting axial movement of the shaft 27A for adjustment purposes as above described.

If desired, the phase relationship between the crankshaft and each of the intake valve camshaft and the exhaust valve camshaft can be adjusted if desired. This can be done, for example, by providing an overriding control input for shaft 21A similar to the control structure for shaft 22A in FIG. 7.

The control input for effecting axial movement of the shaft 27 or shaft 27A can of course be provided manually or it can be provided in response to a device for sensing an engine operating condition. A variety of different engine operating conditions can be sensed in order to provide the control input and thereby effect the variation of the valve timing events as discussed above. Among the engine operating conditions that can be sensed in order to control the valve timing events, there can be enumerated the intake manifold pressure,

the throttle position, the output torque of the engine, the peak cylinder pressure, the exhaust gas temperature and the engine speed. It will be understood that the present invention is not limited to the sensing of any specific engine operating condition as a variety of different operating conditions can be sensed. However, for illustrative purposes, there have been illustrated in FIGS. 8 and 9 two representative ways of sensing an engine operating condition and utilizing same in order to control and adjust the valve timing events of the engine.

Referring to FIG. 8, there is schematically illustrated an engine 31 having an intake manifold 32 and an exhaust manifold 33. The shaft 27 is connected by any suitable means to the piston rod 34 of a piston and cylinder assembly 36. A spring 38 continuously acts on the piston to urge the rod 34, and thereby the shaft 27, in one axial direction. A conduit 37 extends from the intake manifold 32 to the cylinder 36 so that the vacuum in the intake manifold is effective to act on the piston contrary to the urging of the spring. Thus, the

axial position of the shaft 27 and thereby the valve timing events are responsive to the intake manifold vacuum.

FIG. 9 illustrates an alternate structure. The parts in this FIGURE corresponding to parts previously described with respect to FIG. 8 are identified by the same reference numerals with the suffix A added thereto. In this embodiment, a valve 41 is connected between a pressure source 42 and the conduit 37A. The valve has two grooves 43 and 44 which are separated by a land 45. The pressure source is connected to a central passageway 48 in the valve spool and said central passageway communicates with the two grooves 43 and 44. The spool can be moved axially against the urging of a spring 51 by means of a throttle member 52. Thus, when the engine is operating at idling or low speeds in which the throttle member is in the position illustrated in FIG. 9, the fluid pressure source 42 communicates through passageway 48, groove 43 and conduit 37A with the cylinder 36 in order to maintain the shaft 27 in one position. When the throttle member is depressed slightly, as during under moderate speed and moderate acceleration conditions, communication between the source 42 and the conduit 37A is cut off by land 45 and the spring 38 is effective to position the drive shaft 27 in its opposite position to thereby change the valve timing. However, when the throttle member is further depressed, as when it is desired to operate under maximum acceleration or maximum speed conditions, communication from the reservoir to the conduit is re-established through groove 44 and the drive shaft 27 is repositioned in its original position. Thus, according to the embodiment of FIG. 9, the drive shaft can be positioned two different positions corresponding to the two different valve timing sequences that may be desired in the engine for the reasons discussed above.

The control systems of FIGS. 8 and 9 are shown as being used to effect an automatic control of the valve timing adjustment mechanisms illustrated in FIGS. 6 and 7. Thus, the valve timing events can be automatically adjusted to minimize pollutants in the exhaust gas while maintaining effective and efficient operation of the engine.

Although particular preferred embodiments of the invention have been described, the invention contemplates such changes or modifications therein as lie within the scope of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising the steps of:

sensing an engine operation condition;

varying the time of the exhaust means closing with respect to the position of the piston in said cylinder in response to said sensed engine operating condition and thereby adjusting the amount of exhaust gas present within the cylinder for the next combustion, so that there is present in said cylinder:

a small amount of said exhaust gas to provide for a small dilution of the incoming fuel-air charge at light engine loads;

a larger amount of said exhaust gas to provide a greater dilution ,of the incoming fuel-air charge at heavier engine loads; and

a third amount of said exhaust gas, which third amount is smaller than said larger amount, to provide for a reduction in the dilution of the incoming fuel-air charge as engine loading approaches maximum load; said exhaust gas present in said cylinder containing a high concentration of incompletely burned fuel;

mixing the exhaust gas present in the cylinder with the incoming fuel-air charge during the intake stroke for the next cycle; and

igniting the mixture.

2. A method according to claim 1, in which the third amount of said exhaust gas is substantially equal to said small amount to provide for a reduction in the dilution of the incoming fuel-air charge as engine loading approaches maximum load.

3. A method according to claim 1, in which the third amount of said exhaust gas is smaller than said small amount to provide for a reduction in the dilution of the incoming fuel-air charge as engine loading approaches maximum load.

4. Apparatus for minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising:

adjustment means for varying the time of closing of the exhaust means with respect to the position of the piston in the cylinder in order to adjust the amount of exhaust gas present in the cylinder for the next combustion;

control means coupled to said adjustment means for effecting operation thereof, said control means being actuatable in correspondence with engine operating conditions between first, second and third conditions in which said adjustment means is respectively positioned so that the amount of exhaust gas present in said cylinder for the next combustion is l. a small amount at light engine loads,

2. a larger amount at heavier engine loads, and

3. a third amount which is smaller than said larger amount as the engine loading approaches maximum load.

5. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising the steps of:

sensing an engine operation condition;

varying the time of the exhaust means closing with respect to the position of the piston in said cylinder in response to said sensed engine operation condition between an exhaust means closing time ahead of the top dead center position of said piston in said cylinder and an exhaust means closing time at v or after the top dead center position of said piston in said cylinder and thereby adjusting the amount of exhaust gas retained within said cylinder for the next combustion, said retained exhaust gas containing a high concentration of incompletely burned fuel, said varying of the time of the exhaust means closing being carried out so that there is present in the cylinder (a) a small amount of said exhaust gas to provide a small dilution of the incoming fuel-air charge at light engine loads, and (b) a larger amount of said exhaust gas to provide a greater dilution of the incoming fuel-air charge at heavier engine loads;

opening said intake means at least as early as the closing of said exhaust means to admit a fuel-air charge into said cylinder;

mixing said retained amount of exhaust gas with the incoming fuel-air charge during the intake stroke for the next cycle; and

igniting the combined mixture.

6. A method according to claim 5, in whichthe exhaust means closing time is varied by adjusting the phase relationship between the engine crankshaft and a control device for the exhaust means.

7. A method according to claim 6, including the step of adjusting the phase relationship between the engine crankshaft and the control device for the intake means simultaneously with and to the same extent as the adjustment of the phase relationship between said crankshaft and the control device for said exhaust means.

8. A method according to claim 5, in which the exhaust means closing time is varied by adjusting the phase relationship between the engine crankshaft and the exhaust means camshaft.

9. A method according to claim 5, in which the exhaust means closing time is varied by adjusting the phase relationship between the engine crankshaft and the driving means for said exhaust means.

10. A method according to claim 5, in which the intake means is always opened a selectable period of time before the exhaust means is closed in order to provide an overlap period for said intake means and said exhaust means of selected length and in which the intake means opening time is adjusted in the same direction and to the same extent as the exhaust means closing time so as to maintain a constant overlap.

period is changed when the exhaust means closing time is varied.

12. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft,-exhaust means movable between an open and aclosed position and intake means movable between an open and a closed position, said method comprising the steps of:

sensing an engine operation condition; varying, with respect to the position of the piston, in said cylinder, the time of movement of one of said means from one of its positions to the other of its positions in response to said sensed engine operation condition in a manner to selectively adjust the amount of exhaust gas which is not expelled through said exhaust means during the exhaust stroke, said varying of the timeof such movement being carried out so that a. at light engine loads a small amount of said exhaust gas is not expelled through said exhaust means to provide a small dilution of the incoming fuel-air charge, and at heavier engine loads a larger amount of said exhaust gas is not expelled through said exhaust means-to provide a greater dilution of the incoming fuel-air charge; opening said intake means at least as early as the closing of said exhaust means to admit a fuel-air charge into said cylinder; 1 mixing said nonexpelled amount of exhaust gas with the incoming fuel-air charge during the intake stroke for the next cycle; and igniting the combined mixture. 13. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a

crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising the steps of:

sensing an engine operation condition;

varying the timing of at least one of said means with respect to the position of the piston in said cylinder in response to said sensed engine operation condition in a manner to selectively adjust the amount of exhaust gas expelled through said exhaust means during the exhaust stroke, such varying being carried out so that at light engine loads, a small amount of said exhaust gas is not expelled through said exhaust means to provide for a small dilution of the incoming fuel air charge;

at heavier engine loads, a larger amount of said exhaust gas is not expelled through said exhaust means to provide a greater dilution of the incoming fuel-air charge; and

as engine loading approaches maximum load, a third amount of said exhaust gas, which third amount is smaller than said larger amount, is not expelled through said exhaust means to provide for a reduction in the dilution of the incomin fuel-air charge; mixing said non-expelled amount 0 exhaust gas with the incoming fuel-air charge during the intake stroke for the next cycle; and

igniting the mixture.

14. Apparatus for minimizing the amounts ofaundesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder .of said engine, comprising:

adjustment means for varying the timing of at least one of said means with respect to the position of the piston in the cylinder in a manner to selectively adjust the amount of exhaust gas expelled through said exhaust means during the exhaust stroke; and control means coupled to said adjustment means for effecting operation thereof, said control means being actuatable in correspondence with an engine operation condition between first, second and third conditions in which said adjustment means is respectively positioned so that the amount of exhaust gas not expelled through said exhaust means IS a small amount at light engine loads, a larger amount at heavier engine loads, and a third amount which is smaller than said larger amount as the engine loading approaches maximum load.

UNI- 

1. a small amount at light engine loads,
 1. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising the steps of: sensing an engine operation condition; varying the time of the exhaust means closing with respect to the position of the piston in said cylinder in response to said sensed engine operating condition and thereby adjusting the amount of exhaust gas present within the cylinder for the next combustion, so that there is present in said cylinder: a small amount of said exhaust gas to provide for a small dilution of the incoming fuel-air charge at light engine loads; a larger amount of said exhaust gas to provide a greater dilution of the incoming fuel-air charge at heavier engine loads; and a third amount of said exhaust gas, which third amount is smaller than said larger amount, to provide for a reduction in the dilution of the incoming fuel-air charge as engine loading approaches maximum load; said exhaust gas present in said cylinder containing a high concentration of incompletely burned fuel; mixing the exhaust gas present in the cylinder with the incoming fuel-air charge during the intake stroke for the next cycle; and igniting the mixture.
 1. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising the steps of: sensing an engine operation condition; varying the time of the exhaust means closing with respect to the position of the piston in said cylinder in response to said sensed engine operating condition and thereby adjusting the amount of exhaust gas present within the cylinder for the next combustion, so that there is present in said cylinder: a small amount of said exhaust gas to provide for a small dilution of the incoming fuel-air charge at light engine loads; a larger amount of said exhaust gas to provide a greater dilution of the incoming fuel-air charge at heavier engine loads; and a third amount of said exhaust gas, which third amount is smaller than said larger amount, to provide for a reduction in the dilution of the incoming fuel-air charge as engine loading approaches maximum load; said exhaust gas present in said cylinder containing a high concentration of incompletely burned fuel; mixing the exhaust gas present in the cylinder with the incoming fuel-air charge during the intake stroke for the next cycle; and igniting the mixture.
 1. a small amount at light engine loads,
 2. A method according to claim 1, in which the third amount of said exhaust gas is substantially equal to said small amount tO provide for a reduction in the dilution of the incoming fuel-air charge as engine loading approaches maximum load.
 2. a larger amount at heavier engine loads, and
 2. a larger amount at heavier engine loads, and
 3. A method according to claim 1, in which the third amount of said exhaust gas is smaller than said small amount to provide for a reduction in the dilution of the incoming fuel-air charge as engine loading approaches maximum load.
 3. a third amount which is smaller than said larger amount as the engine loading approaches maximum load.
 3. a third amount which is smaller than said larger amount as the engine loading approaches maximum load.
 4. Apparatus for minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising: adjustment means for varying the time of closing of the exhaust means with respect to the position of the piston in the cylinder in order to adjust the amount of exhaust gas present in the cylinder for the next combustion; control means coupled to said adjustment means for effecting operation thereof, said control means being actuatable in correspondence with engine operating conditions between first, second and third conditions in which said adjustment means is respectively positioned so that the amount of exhaust gas present in said cylinder for the next combustion is
 5. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising the steps of: sensing an engine operation condition; varying the time of the exhaust means closing with respect to the position of the piston in said cylinder in response to said sensed engine operation condition between an exhaust means closing time ahead of the top dead center position of said piston in said cylinder and an exhaust means closing time at or after the top dead center position of said piston in said cylinder and thereby adjusting the amount of exhaust gas retained within said cylinder for the next combustion, said retained exhaust gas containing a high concentration of incompletely burned fuel, said varying of the time of the exhaust means closing being carried out so that there is present in the cylinder (a) a small amount of said exhaust gas to provide a small dilution of the incoming fuel-air charge at light engine loads, and (b) a larger amount of said exhaust gas to provide a greater dilution of the incoming fuel-air charge at heavier engine loads; opening said intake means at least as early as the closing of said exhaust means to admit a fuel-air charge into said cylinder; mixing said retained amount of exhaust gas with the incoming fuel-air charge during the intake stroke for the next cycle; and igniting the combined mixture.
 6. A method according to claim 5, in which the exhaust means closing time is varied by adjusting the phase relationship between the engine crankshaft and a control device for the exhaust means.
 7. A method according to claim 6, including the step of adjusting the phase relationship between the engine crankshaft and the control device for the intake means simultaneously with and to the same extent as the adjustment of the phase relationship between said crankshaft and the control device for said exhaust means.
 8. A method according to claim 5, in which the exhaust means closing time is varied by adjusting the phase relationship between the engine crankshaft and the exhaust means camshaft.
 9. A method according to claim 5, in which the exhaust means closing time is varied by adjusting the phase relationship between the engine crankshaft and the driving means for said exhaust means.
 10. A method according to claim 5, in which the intake means is always opened a selectable period of time before the exhaust means is closed in order to provide an overlap period for said intake means and said exhaust means of selected length and in which the intake means opening time is adjusted in the same direction and to the same extent as the exhaust means closing time so as to maintain a constant overlap.
 11. A method according to claim 5, in which the intake means is opened a selectable period of time before the exhaust means is closed to provide an overlap period for said intake means and said exhaust means of selected length and in which the duration of the overlap period is changed when the exhaust means closing time is varied.
 12. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means movable between an open and a closed position and intake means movable between an open and a closed position, said method comprising the steps of: sensing an engine operation condition; varying, with respect to the position of the piston, in said cylinder, the time of movement of one of said means from one of its positions to the other of its positions in response to said sensed engine operation condition in a manner to selectively adjust the amount of exhaust gas which is not expelled through said exhaust means during the exhaust stroke, said varying of the time of such movement being carried out so that a. at light engine loads a small amount of said exhaust gas is not expelled through said exhaust means to provide a small dilution of the incoming fuel-air charge, and b. at heavier engine loads a larger amount of said exhaust gas is not expelled through said exhaust means to provide a greater dilution of the incoming fuel-air charge; opening said intake means at least as early as the closing of said exhaust means to admit a fuel-air charge into said cylinder; mixing said non-expelled amount of exhaust gas with the incoming fuel-air charge during the intake stroke for the next cycle; and igniting the combined mixture.
 13. A method of minimizing the amounts of undesirable obnoxious pollutants emitted from a cyclic internal combustion engine having a piston, a cylinder, a crankshaft, exhaust means and intake means, after combustion of a fuel-air charge within the cylinder of said engine, comprising the steps of: sensing an engine operation condition; varying the timing of at least one of said means with respect to the position of the piston in said cylinder in response to said sensed engine operation condition in a manner to selectively adjust the amount of exhaust gas expelled through said exhaust means during the exhaust stroke, such varying being carried out so that at light engine loads, a small amount of said exhaust gas is not expelled through said exhaust means to provide for a small dilution of the incoming fuel-air charge; at heavier engine loads, a larger amount of said exhaust gas is not expelled through said exhaust means to provide a greater dilution of the incoming fuel-air charge; and as engine loading approaches maximum load, a third amount of said exhaust gas, which third amount is smaller than said larger amount, is not expelled through said exhaust means to provide for a reduction in the dilution of the incoming fuel-air charge; mixing said non-expelled amount of exhaust gas with the incoming fuel-air charge during the intake stroke for the next cycle; and igniting the mixture. 